Animal slaughter is the killing of nonhuman animals, usually referring to killing domesticlivestock. In general, the animals would be killed for food; however, they might also be slaughtered for other reasons such as being diseased and unsuitable for consumption.

The use of a sharpened blade for the slaughtering of livestock has been practiced throughout history. Prior to the development of electric stunning equipment, some species were killed by simply striking them with a blunt instrument, sometimes followed by exsanguination with a knife.

The belief that this was unnecessarily cruel and painful to the animal eventually led to the adoption of specific stunning and slaughter methods in many countries. One of the first campaigners on the matter was the eminent physician, Benjamin Ward Richardson, who spent many years of his later working life developing more humane methods of slaughter as a result of attempting to discover and adapt substances capable of producing general or local anaesthesia to relieve pain in people. As early as 1853, he designed a chamber that could kill animals by gassing them. He also founded the Model Abattoir Society in 1882 to investigate and campaign for humane methods of slaughter, and experimented with the use of electric current at the Royal Polytechnic Institution.[1]

The development of stunning technologies occurred largely in the first half of the twentieth century. In 1911, the Council of Justice to Animals (later the Humane Slaughter Association) was established in England to improve the slaughter of livestock.[2] In the early 1920s, the HSA introduced and demonstrated a mechanical stunner, which led to the adoption of humane stunning by many local authorities.[3]

A pig being slaughtered in Italy

The HSA went on to play a key role in the passage of the Slaughter of Animals Act 1933. This made the mechanical stunning of cows and electrical stunning of pigs compulsory, with the exception of Jewish and Muslim meat.[3][4] Modern methods, such as the captive bolt pistol and electric tongs were required and the Act's wording specifically outlawed the poleaxe. The period was marked by the development of various innovations in slaughterhouse technologies, not all of them particularly long-lasting.

Many countries have adopted the principle of a two-stage process for the non-ritual slaughter of animals. This is to ensure a rapid death with minimal suffering. The first stage of the process, usually called stunning, renders the animal unconscious, and thus not susceptible to pain, but not necessarily dead. In the second stage, the animal is killed. Countries differ in the methods which have been legalized for different species or different ages, some regulations being governmental, others being religious.

This method can be used for sheep, calves and swine. The animal is asphyxiated by the use of CO2 gas before being killed. In several countries, CO2 stunning is mainly used on pigs. A number of pigs enter a chamber which is then sealed and filled with 80% to 90% CO2 in air. The pigs lose consciousness within 13 to 30 seconds. Research has produced conflicting results with some showing pigs tolerate CO2 stunning and others showing they do not.[5][6][7]

Various concentrations of argon and nitrogen have been used to induce unconsciousness, often in conjunction with CO2. Domestic turkeys are averse to high concentrations of CO2 (72% CO2 in air) but not low concentrations (a mixture of 30% CO2 and 60% argon in air with 3% residual oxygen).[8]

This method can be used for sheep, swine, goats, calves, cattle, horses, mules, and other equines. A captive bolt pistol is applied to the head of the animal to quickly render them unconscious before being killed. There are three types of captive bolt pistols, penetrating, non-penetrating and free bolt. The use of penetrating captive bolts has, largely, been discontinued in commercial situations to minimize the risk of transmission of disease when parts of the brain enter the bloodstream.

Mechanical (gunshot/free bullet)

This method can be used for cattle, calves, sheep, swine, goats, horses, mules, and other equines. A conventional firearm is used to fire a bullet into the brain of the animal to render the animal quickly unconscious (and presumably dead). A second method may be used (e.g. drug administration) to ensure the animal is dead.

In Canada, the handling and slaughter of food animals is a shared responsibility of the Canadian Food Inspection Agency (CFIA), industry, stakeholders, transporters, operators and every person who handles live animals. Canadian law requires that all federally registered slaughter establishments ensure that all species of food animals are handled and slaughtered humanely. The CFIA verifies that federal slaughter establishments are compliant with the Meat Inspection Regulations. The CFIA's humane slaughter requirements take effect when the animals arrive at the federally registered slaughter establishment. Industry is required to comply with the Meat Inspection Regulations for all animals under their care. The Meat Inspection Regulations define the conditions for the humane slaughter of all species of food animals in federally registered establishments. Some of the provisions contained in the regulations include:

guidelines and procedures for the proper unloading, holding and movement of animals in slaughter facilities

requirements for the segregation and handling of sick or injured animals

Animal slaughter in the UK is governed under both its own laws and EU law regarding slaughter. The Department for Environment, Food and Rural Affairs (Defra) is the main governing body responsible for legislation and codes of practice covering animal slaughter in the UK.

In the UK the methods of slaughter are largely the same as those used in the United States with some differences. The use of captive bolt equipment and electrical stunning are approved methods of stunning sheep, goats, cattle and calves for consumption[10]- with the use of gas reserved for swine.[12]

Each of these methods is outlined in detail, and the regulations require that inspectors identify operations which cause "undue" "excitement and discomfort" of animals.

In 1958, the law that is enforced today by the USDA Food Safety and Inspection Service (FSIS) was passed as the Humane Slaughter Act of 1978. This Act requires the proper treatment and humane handling of all food animals slaughtered in USDA inspected slaughter plants. It does not apply to chickens or other birds.[14]

Ritual slaughter is the over-arching term accounting for various methods of slaughter used by religions around the world for food production. While keeping religious autonomy, these methods of slaughter, within the United States, are governed the Humane Slaughter Act and various religion-specific laws, most notably, Shechita and Dhabihah.

Animal slaughter in Judaism falls in accordance to the religious law of Shechita. In preparation, the animal being prepared for slaughter must be considered kosher before the act of slaughter can commence and consumed. The basic law of the Shechita process requires the rapid and uninterrupted severance of the major vital organs and vessels. This produces a quick drop in blood pressure, restricting blood to the brain. This abrupt loss of pressure results in the rapid and irreversible cessation of consciousness and sensibility to pain (a requirement held in high regard by most institutions.)[15]

Animal slaughtering in Islam is in accordance with the Qur’an. To slaughter an animal is to cause it to pass from a living state to a dead state. For the meat to be lawful (Halal) according to Islam, it must come from an animal which is a member of a lawful species and it must be ritually slaughtered, i.e. according to the Law, or the sole code recognized by the group as legitimate. There are three methods of killing: slitting the throat (dabh), plunging the knife into the dimple over the breast bone (nahr), and killing in some other way ('aqr). The slaughterer must say the name of God (bismillah), before slaughtering the animal.[16] Blood must be drained out of the carcass. The use of electronarcosis to stun the animal before bleeding it has been approved by the Egyptian Fatwa Committee. [17]

There has been controversy over whether or not animals should be slaughtered and over the various methods used. Some people believe sentient beings should not be harmed regardless of the purpose. Religious slaughter laws and practices have always been a subject of debate, and the certification and labeling of meat products remain to be standardized. Animal welfare concerns are being addressed to improve slaughter practices by providing more training and new regulations. There are differences between conventional and religious slaughter practices, although both have been criticized on grounds of animal welfare. Concerns about religious slaughter focus on the stress caused during the preparation stages before the slaughtering, pain and distress that may be experienced during and after the neck cutting and a the worry of a prolonged period of time of lost brain function during the points between death and preparation if a stunning technique such as electronarcosis is not applied.[18]